The effect of a paramagnetic metal ion within a molecule: comparison of the structurally identical paramagnetic [3,3-Fe(1,2-C2B9H11)2]- with the diamagnetic [3,3-Co(1,2-C2B9H11)2]- sandwich complexes

Derivatives of the ferrabisdicarbollide [3,3'-Fe(1,2-C2B9H11)(2)](-) have been produced starting from the zwitterion [3,3'-Fe(8-(OCH2CH2)(2) -1,2-C2B9H10)(1',2'-C2B9H11)], 1, upon reaction with nucleophiles: alkoxides, halides and hydrosulfide ions HS-. The result has been the preparation of [3,3'-Fe(8-(OCH2CH2)(2)R/X-1,2-C2B9H10)( 1',2'-C2B9H11)] (R = OMe, [2](-); OEt, [3](-); OCH2CH2OCH3, [4](-); and X = Cl, [5](-); Br, [6](-); I, [7](-); and SH, [8](-)). The reaction behavior of 1 is comparable to the well-studied cobalt equivalent, [3,3'-Co(8-(OCH2CH2)(2)-1,2-C2B9H10)(1',2'-C2B9H11)], and the yields and stability of the resulting complexes are similar. These results are relevant taking into account that [3,3'-Fe(1,2-C2B9H11)(2)](-) is a paramagnetic anion. Implications of this are observed in the B-11-, H-1 and C-13 NMR spectra of [3,3'-Co(1,2-C2B9H11)(2)](-) and [3,3'-Fe(1,2-C2B9H11)(2)](-) that having identical sandwich molecular structures and the same negative charge have absolutely different widths of the NMR field, between 15 and -25 ppm for [3,3'-Co(1,2-C2B9H11)(2)](-) and in the range 150 to -550 ppm for [3,3'-Fe(1,2-C2B9H11)(2)](-). The sharpness of both spectra is on the other hand comparable, although no B-H couplings are observed in the Fe metallacarborane or its derivatives. Remarkable is the comparative influence vs. [3,3'-Co(1,2-C2B9H11)(2)](-) of replacing Co by Fe on the elements of the cluster layer nearest to the metal. The two equivalent C cluster (C-c) atoms are influenced at 36 840 Hz, the two equivalent B atoms that are adjacent to the two C-c are influenced at 38 157 Hz and the single B that is adjacent to the two B atoms is influenced at 44 062 Hz. Remarkable is the similar influence on B and on C, taking into account that the values have been obtained from two distinct NMR spectra of B-11 and C-13. The {B-11-B-11} COSY NMR and {H-1-B-11} HETEROCOSY NMR spectra of [3,3'-Fe(1,2-C2B9H11)(2)](-) have been obtained and are reported for the first time.